package com.greendizer.api.util;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Collection;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

/**
 * A utility class for parsing and formatting HTTP dates as used in cookies and
 * other headers. This class handles dates as defined by RFC 2616 section 3.3.1
 * as well as some other common non-standard formats.
 * 
 * @author Christopher Brown
 * @author Michael Becke
 */
public final class DateUtil {

  /**
   * Date format pattern used to parse HTTP date headers in RFC 1123 format.
   */
  public static final String PATTERN_RFC1123 = "EEE, dd MMM yyyy HH:mm:ss zzz";

  /**
   * Date format pattern used to parse HTTP date headers in RFC 1036 format.
   */
  public static final String PATTERN_RFC1036 = "EEEE, dd-MMM-yy HH:mm:ss zzz";

  /**
   * Date format pattern used to parse HTTP date headers in ANSI C
   * <code>asctime()</code> format.
   */
  public static final String PATTERN_ASCTIME = "EEE MMM d HH:mm:ss yyyy";

  private static final Collection<String> DEFAULT_PATTERNS = Arrays
      .asList(new String[] { PATTERN_ASCTIME, PATTERN_RFC1036, PATTERN_RFC1123 });

  private static final Date DEFAULT_TWO_DIGIT_YEAR_START;

  static {
    Calendar calendar = Calendar.getInstance();
    calendar.set(2000, Calendar.JANUARY, 1, 0, 0);
    DEFAULT_TWO_DIGIT_YEAR_START = calendar.getTime();
  }

  private static final TimeZone GMT = TimeZone.getTimeZone("GMT");

  /**
   * This class should not be instantiated.
   */
  private DateUtil() {
  }

  /**
   * Parses a date value. The formats used for parsing the date value are
   * retrieved from the default http params.
   * 
   * @param dateValue
   *          the date value to parse
   * @return the parsed date
   * @throws DateParseException
   *           if the value could not be parsed using any of the supported date
   *           formats
   */
  public static Date parseDate(String dateValue) {
    return parseDate(dateValue, null, null);
  }

  /**
   * Parses the date value using the given date formats.
   * 
   * @param dateValue
   *          the date value to parse
   * @param dateFormats
   *          the date formats to use
   * @return the parsed date
   * @throws DateParseException
   *           if none of the dataFormats could parse the dateValue
   */
  public static Date parseDate(String dateValue, Collection<String> dateFormats) {
    return parseDate(dateValue, dateFormats, null);
  }

  /**
   * Parses the date value using the given date formats.
   * 
   * @param dateValue
   *          the date value to parse
   * @param dateFormats
   *          the date formats to use
   * @param startDate
   *          During parsing, two digit years will be placed in the range
   *          <code>startDate</code> to <code>startDate + 100 years</code>. This
   *          value may be <code>null</code>. When <code>null</code> is given as
   *          a parameter, year <code>2000</code> will be used.
   * @return the parsed date
   * @throws DateParseException
   *           if none of the dataFormats could parse the dateValue
   */
  public static Date parseDate(String dateValue,
      Collection<String> dateFormats, Date startDate) {

    if (dateValue == null) {
      throw new IllegalArgumentException("dateValue is null");
    }
    if (dateFormats == null) {
      dateFormats = DEFAULT_PATTERNS;
    }
    if (startDate == null) {
      startDate = DEFAULT_TWO_DIGIT_YEAR_START;
    }
    // trim single quotes around date if present
    // see issue #5279
    if (dateValue.length() > 1 && dateValue.startsWith("'")
        && dateValue.endsWith("'")) {
      dateValue = dateValue.substring(1, dateValue.length() - 1);
    }

    SimpleDateFormat dateParser = null;
    for (String format : dateFormats) {
      if (dateParser == null) {
        dateParser = new SimpleDateFormat(format, Locale.US);
        dateParser.setTimeZone(TimeZone.getTimeZone("GMT"));
        dateParser.set2DigitYearStart(startDate);
      } else {
        dateParser.applyPattern(format);
      }
      try {
        return dateParser.parse(dateValue);
      } catch (ParseException pe) {
        // ignore this exception, we will try the next format
      }
    }

    // we were unable to parse the date
    throw new RuntimeException("Unable to parse the date " + dateValue);
  }

  /**
   * Formats the given date according to the RFC 1123 pattern.
   * 
   * @param date
   *          The date to format.
   * @return An RFC 1123 formatted date string.
   * @see #PATTERN_RFC1123
   */
  public static String formatDate(Date date) {
    return formatDate(date, PATTERN_RFC1123);
  }

  /**
   * Formats the given date according to the specified pattern. The pattern must
   * conform to that used by the {@link SimpleDateFormat simple date format}
   * class.
   * 
   * @param date
   *          The date to format.
   * @param pattern
   *          The pattern to use for formatting the date.
   * @return A formatted date string.
   * @throws IllegalArgumentException
   *           If the given date pattern is invalid.
   * @see SimpleDateFormat
   */
  public static String formatDate(Date date, String pattern) {
    if (date == null) {
      throw new IllegalArgumentException("date is null");
    }
    if (pattern == null) {
      throw new IllegalArgumentException("pattern is null");
    }

    SimpleDateFormat formatter = new SimpleDateFormat(pattern, Locale.US);
    formatter.setTimeZone(GMT);
    return formatter.format(date);
  }

}